Abstract

In this chapter, the authors have described in detail the microsurgical anatomy of posterior incisure space. All the anatomical landmarks and surgical relations are depicted and discussed.

Keywords: pineal region, supracerebellar approach, tentorial incisure, brain stem cavernoma

43.1 Introduction

The posterior incisural space corresponds to the posterior part of the tentorial hiatus, which mainly comprise the posterior part of the rostral brainstem, the pineal region, and splenium of the corpus callosum. Consequently, the anatomical approaches described herein are aimed at deep-seated brain lesions. These pathologies lie deep in the brain and they relate to a number of eloquent structures. Management requires a thorough knowledge of the microsurgical anatomy of the structures surrounding the posterior midbrain and the pineal region areas. The complex of veins that drain toward the vein of Galen pose a particular challenge, and they may eventually determine the best surgical approach. By definition, these approaches are long corridors that require fine microsurgical technique, high visual magnification, and most often, neuronavigation aid. Furthermore, it requires meticulous surgical planning. The use of the surgical endoscope is a powerful aid to inspect “blind spots” in various loci, including the posterior incisural space. The use of the endoscope is well established to treat hydrocephalus associated with tumors, as well as in obtaining biopsy tissue for pathology analysis. A literature review didn’t find robust evidence, stating that the endoscopic resection alone of pineal region pathologies is the current standard of care. Therefore, we will focus on the complex microsurgical anatomy of this region, as well as corridors available for using the operating microscope.

43.2 Objective

The objectives are to describe, in detail, the microsurgical anatomy relevant to pathologies arising in the posterior incisural space; describe the surgical corridors used to approach these lesions; and discuss complication avoidance when dealing with lesions in this area. The anatomy will be shown through cadaveric dissections carried out at the Barrow Neurological Institute^®, Phoenix, AZ. The specimens have been injected with red or blue latex to highlight brain arteries and veins, respectively. The surgical approaches to the posterior incisural space are presented. Illustrative cases have been carried out by the senior author.

43.3 Microsurgical Anatomy

The microsurgical anatomy of the posterior tentorial space will be presented in detail. It provides the basis to understand and perform the surgical approaches used to deal with a number of lesions in this area. Surgical approaches to this area are divided into two basic categories: supratentorial approaches and infratentorial approaches. Supratentorial approaches are as follows:

●The area between the medial surface of the parieto-occipital lobes and the falx, with sectioning of the corpus callosum and with/without sectioning of the tentorial: the posterior interhemispheric transcallosal approach/the posterior interhemispheric transcallosal transtentorial approach

●The area between the falx, the anterior interhemispheric fissure, and midline dissection of the fornix: the interhemispheric transcallosal midline interfornicial approach to the third ventricle; or the transchoroidal approach to the third ventricle

●The area between the medial and basal occipital lobe and the falx, and above the tentorium with/without sectioning of the tentorial: the suboccipital supratentorial approach/the suboccipital transtentorial approach

○The supratentorial approaches are located above the deep venous complex.

Infratentorial approaches comprise the following approaches:

●Below the tentorium and above the superior surface of the cerebellum: the midline infratentorial supracerebellar approach (MISA)

●Below the tentorium, and above the tentorial surface of the cerebellum at paramedian, lateral, and far-lateral positions: the ISA approach, paramedian, lateral, and far-lateral (PSIA, LSIA, FLSIA, respectively)

●Below the tentorium and above the superior surface of the cerebellum with sectioning of the tentorial: the supracerebellar transtentorial approach

○These approaches are directed inferior to the deep complex of veins.

The transcallosal approaches are often useful approaches, but they must be considered especially if lesions extend anterior in relation to the third ventricle, or into the lateral ventricles. A combination of more than one surgical corridor may be necessary.

The anatomy of the medial occipital lobe, the basal occipital lobe, the tentorium and the tentorial hiatus, and the superior or tentorial surface of the cerebellum are presented in detail. The anatomical structures that lie deep in the posterior tentorial space are also shown in detail.

Fig. 43.1Lateral view of the right hemisphere on an anatomical specimen. The left hemisphere has been removed, and the left midbrain has been left in place. The anterior, the middle, and the posterior incisural spaces are shown. Suboccipital craniotomies, especially if combined with sectioning of the tentorium, may reach the posterior and the lateral aspect of the cerebral peduncle, the uncus, and corresponding portions of the medial temporal lobe. On the other hand, these structures cannot be approached via posterior temporal lobe elevation due to the presence of the vein of Labbé.

43.4 Overview

43.4.1 The Posterior Incisural Space